Fabrication of gas discharge display devices generally of the character disclosed herein have been accomplished in the past and typically these are one-for-one type operations. That is, individual glass substrates and/or ceramic substrates are provided upon which the conductor runs are printed and then the dielectric masks are printed over the conductor runs and in the openings in the conductor runs for the cathode electrodes, the cathode materials which interface with the gas discharge medium are printed thereon and all of these being subsequently fired and cured. Such devices are subsequently assembled usually by the use of a gas filling tubulation but in some cases tubulationless devices have been fabricated in which final hermetic seal of two spaced apart substrates accomplished by utilization of an unfused sealing frame, evacuating the entire unit and back filling with an elevated temperature and then heating the assembled parts spaced between the electrode elements while retaining the gas in the assembly until the glass parts have been softened to a sealing temperature to result in a fusion sealing of the frame element and thereby final assembly of the device. This process is difficult and cumbersome and does not lend itself well to batch processing of individual display elements.
In Boswau U.S. Pat. No. 2,142,106, a gaseous discharge display device having small glass discs carrying shaped cathode elements and individual annode elements are stacked in a disc with the interstices between the discs sealed in a manner around the periphery to prevent electrode interference between each other, a small aperture being left at one point in the periphery by leaving out the sealing operation at this point to provide communication with the main gas chamber formed by an overall glass envelope or bulb. In the Boswau patent, the bulb is subsequently exhausted and filled with the gas at a proper pressure, the exhausting and back filling processes extending through and communicating through the aperture to the individual gas chambers formed in the spaced disc and the aperture then is filled with a suitable sealing material which permits the gas to permeate during the exhausting and filling operation thereafter this individual seal element or plug is sealed by heating means of electronic bombardment or other sealing means. The present invention is a direct and distinct improvement over the sealing technique disclosed in the Boswau patent in that the present invention adapts a portion of that technique of the Boswau patent and extends same to batch processing of thousands of individual discrete gaseous discharge panel elements in a manner and fashion not heretofore available, with yield factors significantly greater than those of the prior art. A substantially bubble-free glass rod, shaped generally in the perimetrical configuration of the gas chamber is fused to the two substrate surfaces in an air atmosphere. A small opening or space between the ends of the rod is provided. Large numbers of the device may be stacked in trays, with a small glass rod bridging the ends of the rod and space and held in position by the opposing substrate. The rod seal or plug is slightly smaller in diameter to snugly fit between opposing substrate surfaces and has a fusion temperature slightly below that of the formed rod. Both materials are, however, of optical quality and of substantially bubble-free edge surfaces. This loose rod seal element or plug permits batch vacuumization (also under bake out conditions if desired) and back filling with any desired gas composition of large numbers of individual devices in a single operation.
In the prior art, in making segmented electrode gaseous discharge display panels, particularly alphanumeric type displays, the individual conductor runs are printed first and fired on the substrate and subsequently, the mask and cathode element electrodes e.g., those elements which are to be in direct conductive contact with the gas are printed and cured, the printing of the cathode elements being through the apertures or openings in the dielectric mask. In accordance with this invention, instead of using a ceramic substrate, simple, inexpensive glass substrates are used. The conductor elements forming the cathode electrodes which interface with the gas medium are printed first and cured at relatively higher temperatures so as to eliminate cathode porosity and assure that those conductor segments or elements forming the cathodes of the device have a good hard surface at the gas interface so as to minimize sputtering problems and improve the discharge properties of such devices.
In the sealing operation described earlier herein, it has also been found that the use of screened-on sealing materials in an unfused state, is not as desirable as the use of a preformed rod element fabricated from glasses having fiber optic properties, that is to say no bubbles therein which distort and rupture the seal upon heating and/or vacuumization.
The typical and classical way of fabricating gaseous discharge devices is to vacuum bake the devices so as to remove included gaseous contaminants from the interior surfaces of the device. Vacuum baking is a very time consuming and expensive process. In another feature of the process of this invention, the several thousand devices stacked in trays are placed in a vacuum chamber. The vacuum is pulled over the device without heating to remove substantially all of the free contaminants from the individual gaseous discharge devices and then, at an ambient temperature, the gas filling is admitted to the processing chamber and thereby each individual gaseous discharge element is filled at room or ambient temperature. This assures proper gas proportions and eliminates the need for accurate and precise calibration at high temperatures of the gas filling. Then, after the gas filling has been introduced to the devices, the devices are heated by Calarod heaters inside the chamber so as to effect a melting of small sealing elements in the openings described earlier herein. This technique thereby avoids the long time between the filling and heating of the chamber thereby reducing a production run of thousands of devices in a single chamber to no more than six hours in pumped in heating back filling with the gas and the like. Since this sealing process is done at a pressure somewhat below ambient, and since the volume of gas in the vacuum chamber can be greater than the cumulative gas volume contained in the devices, there is sufficient heating under somewhat negative pressure conditions to assure good clean up of the device under less than perfect vacuum conditions and at significantly reduced cost and processing time. In still another feature of the invention, small mercury-containing capsules or givers are activated by the use of a laser beam. To this end, the device is provided with laser transparent windows in each of two glass substrates which thereby permits the use of a laser beam to effectively break the mercury capsule without damaging the device itself.
Finally, in the prior art, connections between the anode electrodes and exterior connections to operating potentials have been by means of small metal clips between the two substrates. In accordance with this invention a conductive epoxy is inserted between the terminals ends of the anode electrodes and the printed conductor ends on the cathode plate. According to the invention, this epoxy is carefully cured so as to assure that there are no bubbles in contact with the annode elements which would tend to cause hot spots and breaking of the anode connections.